If you have something that is a like a tutorial just create a new posting in the Tutorials and Examples tag and follow @ThomDietrich’s excellent Influx+Grafana as a template for how to structure and present the information.
For the OH 1 docs, just dive in and edit the wiki pages.
For OH 2, post an issue to the openhab-docs github so everyone knows what you are working on, fork the repo and create a new branch for your changes. Then make the changes and issue a pull request when it is done.